Our invention is involved with the formation of a binder system for coatings on surfaces such as glass, metal or wood. In particular, our invention is directed toward a formulation for forming light diffusive coatings on light bulb envelopes utilizing a synergistic combination of colloidal alumina and finely-divided, precipitated silica.
The light emitted from incandescent light bulbs with clear glass envelopes is harsh and can be dangerous to the eyes. This condition has been alleviated by introduction of a means of diffusing light onto or upon the envelope. The most common method of providing light diffusion is to etch the inside of the glass envelope with fluoride ion. The process is dangerous, polluting, and the product is not particularly attractive since the etched glass is gray. Recently, bulbs have been produced with white coatings that are light diffusive. Such coatings are generally formed by attaching pigmentary particles to the glass utilizing electrostatic force. These coatings are considered to be only moderately successful, since they are not mar resistant. Small pieces of glass or even dirt tumbling and rolling within the envelope are sufficient to destroy the coating. For these reasons, handling and shipping of such coated envelopes on a large scale is impractical. The industry has need for a coating which is easy to apply, adheres well to the envelopes wall, is durable, has an attractive appearance and is low in cost.